Department of Otorhinolaryngology-Head and Neck Surgery, Cheonan Hospital, Soonchunhyang University School of Medicine, Cheonan, Korea.

Abstract

OBJECTIVES:

Cisplatin, a widely used chemotherapeutic agent, has serious side effects, including nephrotoxicity and ototoxicity. Minocycline is a semisynthetic second-generation tetracycline that exerts anti-inflammatory and neuroprotective effects. The purpose of this study was to elucidate the protective effect of minocycline against cisplatin-induced ototoxicity in the auditory hair cell.

METHODS:

The House Ear Institute-Organ of Corti 1 (HEI-OC1) cell line and guinea pigs were used for in vitro and in vivo experiments. Cells were exposed to cisplatin with or without pre-treatment with minocycline. Cell survival was analyzed using MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide). Whole-cell lysates were collected and immunoblotted with antibodies against Bcl-2, p-c-Jun, active caspase-3, cleaved poly (ADP-ribose) polymerase (PARP), and apoptosis-inducing factor (AIF). The guinea pigs received intraperitoneal injections of cisplatin alone or following minocycline pretreatment. The auditory brainstem response was tested and the cochleae were harvested and evaluated using scanning electron microscopy.

RESULTS:

Survival significantly increased in cells pretreated with minocycline compared with cells exposed to cisplatin alone. Cisplatin treatment increased the expression of active caspase 3, p-c Jun, PARP, and AIF, and pretreatment with minocycline attenuated this response. In animal study, the threshold shift by cisplatin injection in the auditory brainstem response was less pronounced in animals pretreated with minocycline. Scanning electron microscopy revealed more severe damage to the outer hair cells at the basal and middle turns than the apical turn.

The distribution (A) and mean amount (B) of hearing threshold shift in each group. The shift was greater in group 2 (white circle) than it was in group 1 (black circle). The threshold shift in the 16 Hz tone burst significantly different between the two groups. The threshold shift was less than 10 dB in two animals pretreated with minocycline.

Scanning electron micrographs of the basal turn of the organ of Corti. (A) In a hearing-preserved animal pretreated with minocycline followed by cisplatin treatment, the outer hair cells are well preserved with minimal loss. (B) In an animal treated with cisplatin alone, catastrophic destruction occurred in the outer hair cells with fusion of cilia and bulla formation. The inner hair cells are relatively well preserved compared with the outer hair cells in both groups.